1. Technical Field
The present invention relates to a sensor output IC including a switching element that turns on and off between output terminals based on a detection signal from a sensor, and a sensor device.
2. Related Art
FIG. 6 illustrates a schematic configuration of a general sensor system that performs various operations based on a detection signal from a sensor. As illustrated in FIG. 6, a sensor system 100 has a configuration in which a power supply 111 and a load 112 are connected to a sensor device 110. The power supply 111 is connected to power supplying terminals 113 and 113 of the sensor device 110 to supply an electric power to the sensor device 110. The load 112 performs various operations based on a detection signal from a sensor 120 (described below) by the supply of the electric power, and the power supply 111 and the load 112, connected in series, are connected to output terminals 114 and 114.
In FIG. 6, one side of the power supplying terminals 113 and one side of the output terminals 114 constitute a common ground terminal GND. Hereinafter, positive sides of the power supplying terminal 113 and the output terminal 114 are referred to as a power supplying terminal VCC and an output terminal OUT, respectively.
The sensor device 110 includes the sensor 120 and a sensor output IC (Integrated Circuit) 121. The sensor 120 detects physical or chemical information, and a proximity sensor and a photoelectric sensor can be cited as an example of the sensor 120. The detection signal detected with the sensor 120 is inputted to the sensor output IC 121.
In the sensor output IC 121, output terminals 122 and 122 are connected to the output terminals OUT and GND of the sensor device 110, respectively. The sensor output IC 121 includes a switching element 123 that turns on and off between the output terminals 122 and 122 based on the detection signal from the sensor 120. Therefore, the supply of the electric power from the power supply 111 to the load 112 is turned on and off, which allows the operation of the load 112 to be controlled based on the detection of the sensor 120.
In the sensor system 100 illustrated in FIG. 6, when the load 112 is short-circuited while the switching element 123 becomes an on state, possibly an excess current is passed through the switching element 123 to lead to a malfunction. Therefore, conventionally a load-short-circuit protection function of protecting the switching element 123 from the malfunction even if the load 112 is short-circuited is provided in the sensor device 110.
For example, Japanese Unexamined Patent Publication No. 2-156721 (published on Jun. 15, 1990) discloses a short-circuit protection circuit that forcedly turns off the switching element 123 for a second predetermined time interval when detected that the excess current of a predetermined value or more is continuously passed through the switching element 123 for a first predetermined time interval. In the Japanese Unexamined Patent Publication No. 2-156721, a timer circuit is used to determine whether or not the first and second predetermined time intervals have elapsed. Additionally, there is well known a technique of using a divided frequency of a clock frequency of a logic circuit.
However, for the use of the timer circuit, it is necessary to provide a circuit element having a capacitance or a resistance outside the sensor output IC 121, which results in a circuit scale and production cost being increased in the sensor device 110. For the use of the logic circuit, it is necessary to provide the logic circuit in the sensor output IC 121, which results in a process of producing the sensor output IC 121 being limited to an expensive one to increase the production cost. Thus, the conventional short-circuit protection circuit becomes troublesome in further achieving the miniaturization and low cost of the sensor device 110.